Gsm and RF rejection ...

[djdamix]

Hello,

I'm looking for a good solution to prevent RF and GSM detection with my amplifier, I now it could be done by filtering the input.
The input is a basic differential pair as on the following file :

http://www.diyaudio.com/forums/attachment.php?s=&postid=488146

ps: there is no more DC offset ...


Any advice is welcome.

David

 

[djdamix]

was it a stupid question ? is case of the amplifier supposed to stop all the RF ?

David

 

[boholm]

The problem is that RF can get in anywhere - not just on the input. Also the wires to the speaker are excellent antennas for RF. So if you have a problem with RF you can try the old trick, which is to do one winding round a ferrite core ring or using one of these: . . .wel . . . please do a search on Farnell using this search word "535886". Then you will get the picture

Ohterwise you can make an input filter. I recommend using 1 MHz as cutoff, so you will not interfere with the audio signal too much - fase and amplitude wise.

 

[peranders]

Good RF immunity comes also with a good pcb with groundplane but as a start and good decoupling and a LP-filter at the input.

 

[djk]

You need to add R2 and C1 to your input stage:

http://users.ece.gatech.edu/~mleach/lowtim/instage.html

R2 - 2K

C1 - 390 pF mica (Arco DM15-391J or DigiKey 338-1057-ND

A ceramic cap may be used if nothing else is available.

 

[djdamix]

thanks, I'll try that, I hope my GSM phone won't "sing" in the loudspeaker anymore.